Tungsten alloying element

Niobium is important as an alloy addition in steels (see Steel). This use consumes over 90% of the niobium produced. Niobium is also vital as an alloying element in superalloys for aircraft turbine engines. Other uses, mainly in aerospace appHcations, take advantage of its heat resistance when alloyed singly or with groups of elements such as titanium, tirconium, hafnium, or tungsten. Niobium alloyed with titanium or with tin is also important in the superconductor industry (see High temperature alloys Refractories). 

Mechanical properties depend on the alloying elements. Addition of carbon to the cobalt base metal is the most effective. The carbon forms various carbide phases with the cobalt and the other alloying elements (see Carbides). The presence of carbide particles is controlled in part by such alloying elements such as chromium, nickel, titanium, manganese, tungsten, and molybdenum that are added during melting. The distribution of the carbide particles is controlled by heat treatment of the solidified alloy. 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

Other potential applications are ceramic powders coated with their sintering aids, zirconia coated withyttria stabilizer, tungsten carbide coated with cobalt, or nickel, alumina abrasive powders coated with a relatively brittle second phase such as MgAl204 and plasma spray powders without the segregation of alloying elements. 

About 90 percent of all tungsten alloys are used in mining, construction, and electrical and metal-working machinery. These alloys are used to make high-speed tools heating elements in furnaces parts for aircraft and spacecraft equipment used in radio, television, and radar rock drills metal-cutting tools and similar equipment. 

Thorium is a radioactive element and a natural a-emitter (specific activity 4250 Bq/g and half-life 1.4 x lO a). Health and environmental considerations (evaporation and inhalation of thorium during welding disposal of grinding dust) have therefore in the past led to a partial replacement of thoriated tungsten for welding operations and in the lighting industry by thoria-free ODS tungsten alloys [6.24]. 

The application of tungsten metal which, at the beginning of the 20th century, was used only as a filament in incandescent bulbs and as alloying element in steel, as well as of its alloys, is nowadays very widespread and covers quite different fields such as lighting, electronics, high-temperature technology, medicine, aviation, military uses, sports, and so on. 

Other alloying elements to form complex carbides (MeC, M23C6). The chemistry of these carbides depends on the concentration of carbon and the alloying elements present as well as on the heat treatment applied. For the same level of carbon in the steel tungsten will produce a larger carbide voliune than other allo5ung elements [8.3],... 

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